The Narrator is an unnamed practitioner of mesmerism who seeks to uncover whether hypnosis can delay death in a terminal patient. Utilizing precise medical jargon, he maintains an objective tone to lend scientific credibility to his unorthodox activities. His primary motivation is intellectual curiosity, which prompts him to select a dying acquaintance for his experiment.

M. Ernest Valdemar is an author and translator residing in Harlem, known for publishing Polish texts under the pen name Issachar Marx. He is severely afflicted with phthisis, a disease that leaves him skeletal and plagued by a constant cough. Knowing his time is short and lacking relatives in America to object, he calmly allows his friend to attempt a radical hypnotic procedure on his deathbed.

Mr. Theodore L—l is a medical student recruited to legitimize the bedside mesmerism. His identity is partially anonymized to protect his privacy and to preserve the clinical appearance of a factual report. He sits by the deathbed to take detailed notes on the biological responses observed during the hypnosis.

Drs. D— and F— are the anonymized physicians attending to the terminal patient at his home. They estimate the precise timeline of the fatal illness with cold medical detachment. Rather than objecting to the unorthodox hypnotism, they allow the procedure to proceed out of their own intellectual curiosity since the patient is beyond conventional saving.